1. Field of the Invention
This invention relates to improvements in a construction for an aluminum circuit to be disconnected and method of cutting the same, wherein in a semiconductor device in order to replace defective bits by redundant bits the corresponding aluminum interconnection portion in the circuit is cut.
2. Description of the Prior Art
As for a construction for an aluminum circuit to be disconnected wherein order to replace a faulty bit in a semiconductor memory device the aluminum interconnection portion in the circuit is cut, use has been made of a construction wherein aluminum interconnections are formed on the flat surface of an underlying base formed of an insulating film. As for a method of disconnecting aluminum interconnections, use has been made of a method which consists in applying a laser beam to an aluminum interconnection portion to be cut to thereby evaporate the aluminum for cutting.
FIG. 1 is a perspective view showing the construction of a conventional aluminum circuit to be disconnected. In FIG. 1, the conventional circuit to be disconnected 300 has a construction in which an aluminum interconnection 1 to be cut is formed on the flat surface of an underlying base formed of an insulating film 3. The cutting of conventional aluminum interconnections will now be described with reference to FIG. 1.
A predetermined region of the aluminum interconnection 1 to be cut is irradiated with a laser beam 4 from a laser optics (not shown), whereby the aluminum in the irradiated region is evaporated and the aluminum interconnection 1 is cut. The laser beam 4 used for cutting has a relatively high power and a relatively long irradation time duration in order to evaporate a relatively large amount of aluminum.
The construction of the aforesaid conventional circuit to be disconnected of aluminum interconnection and the method of cutting the same have the following problems.
FIG. 2 is a perspective view for explaining above-said problems, showing scattered aluminum particles produced when an aluminum interconnection is cut. In FIG. 2, there is shown on an insulating film base 3, an aluminum interconnection 1 which has been cut, and also shown are scattered aluminum particles 9 produced by the cutting of the aluminum interconnection.
Heretofore, a laser beam of relatively high power intensity has been used to ensure that the aluminum in the portion of the aluminum interconnection 1 to be cut evaporates quickly. As a result, the evaporated aluminum is scattered over a wide range around the cut portion and solidifies thereon; thus, there has been a problem that the scattered aluminum particles 9 give rise to defects such as current leaks and short circuits between aluminum interconnections in that region.
For prior arts for cutting aluminum interconnections using laser beams, refer to:
(1) Myron J. Rand, "RELIABILITY OF LSI MEMORY CIRCUITS EXPOSED TO LASER CUTTING", 17th annual proceedings, Reliability Physics 1979, pp. 220-225; and
(2) Robert T. Smith et al., "Laser Programmable Redundancy and Yield Improvement in a 64K DRAM", IEEE JOURNAL OF SOLID-STATE CIRCUITS, Vol. SC-16, No. 5, Oct. 1981, pp. 506-514.
The prior art (1) discloses a method in which after an interconnection has been cut by laser, the region is covered with a plasma silicon nitride film.
The prior art (2) discloses a method in which an interconnection is cut using a laser beam having a power of about 10 .mu.J/pulse and an irradiation time duration of about 50 ns.